Imaging device and its manufacturing method

ABSTRACT

An imaging apparatus includes: a three-dimensional substrate in which a partition wall ( 11 ) having an opening ( 10   a ) at a central portion is formed so as to cross an inner cavity; an optical filter ( 5 ) that is fixed on a first flat surface ( 12 ) of both surfaces of the partition wall so as to cover the opening; a semiconductor imaging device ( 4 ) that is face-down mounted on a second flat surface ( 13 ) of the partition wall with an imaging area ( 4   a ) facing the opening; and an optical system for forming images that is installed on a side of the optical filter in the inner cavity of the three-dimensional substrate. The opening of the partition wall is dosed on both sides with the optical filter and the semiconductor imaging device so as to form a cavity. An air passage ( 12   a ) for allowing communication between the cavity and an exterior of the three-dimensional substrate is formed on the first flat surface, and has a labyrinth structure that causes a flow rate of air passing through the air passage to vary depending on a location in the air passage. This allows air circulation between the exterior and a cavity enclosed by a semiconductor imaging device and an optical filter, while suppressing the entry of foreign matter from the exterior into the cavity via an airflow caused by expansion/contraction of air.

TECHNICAL FIELD

The present invention relates to an imaging apparatus using asemiconductor imaging device, which is reduced in size and thickness andused mainly in a camera mounted in portable equipment or the like, and amethod for manufacturing the same.

BACKGROUND ART

Conventional imaging apparatuses of this kind have a structure describedin JP2001-245186 A, for example. In the structure, a semiconductorimaging device configured of a CCD (Charge Coupled Device) or the likeis mounted with a lens on a three-dimensional substrate and converts afocused image formed by the lens into an electric signal so that theimage can be output.

The three-dimensional substrate is composed of a base part having arectangular planar shape and a cylindrical barrel part disposed on anupper portion of the base part, and an opening is formed on a boundarybetween the base part and the barrel part. The lens is fitted against aninner peripheral surface of the barrel part. With an optical axis of thelens being the center, an optical filter is disposed on an upper side ofthe opening, and the semiconductor imaging device is disposed on a lowerside of the opening.

According to the requirement for a size reduction and a higherperformance of portable equipment mounting imaging apparatuses, therehas been an increasing demand that the imaging apparatuses themselves bereduced in size and weight. In order to meet this demand, it has beenthe case that the thickness of each of the above-described components isreduced to the maximum extent, thereby realizing the thickness reductionof imaging apparatuses.

Such a conventional imaging apparatus provides a reduced margin ofstrength due to the thickness reduction of each constituent component.Because of this, in a heating process for bonding or joining, theflatness of a surface of a three-dimensional substrate on which asemiconductor imaging device is mounted is likely to be deteriorated dueto anisotropy in thermal expansion of the substrate and heat distortioncaused in the substrate.

Furthermore, semiconductor imaging devices also should be reduced inthickness, and this has been met by so-called back grinding in which asemiconductor wafer is ground from a back surface thereof with, forexample, a grinder using a diamond grindstone or the like. Because ofthis, the mechanical strength of a semiconductor imaging device itselfis decreased compared with a conventional case, and the strength of athree-dimensional substrate on which the semiconductor imaging device ismounted also is decreased, so that it is more likely that thesemiconductor imaging device and the three-dimensional substrate arewarped due to heat and a load applied at the time of mounting.

As described above, thickness reduction leads to an increase in theoccurrence of a failure in a process, which causes a cost increase, andrequires an inspection process, which increases the number of processes.This has been a hindrance to the thickness reduction of imagingapparatuses. Particularly, with respect to the following problems thatare attributable to an entire module being heated/cooled in a bonding orsealing process for fabricating an imaging apparatus, thicknessreduction exerts a greater influence on the performance of the imagingapparatus.

That is, when an entire module is heated/cooled, expansion/contractionof air is caused in a cavity enclosed by a semiconductor imaging deviceand an optical filter that are installed on a three-dimensionalsubstrate. If there is no air circulation from and to the exterior atthis time, an internal pressure in the cavity increases and may causethe optical filter to be broken. In order to avoid this, conventionally,an air purging hole is provided so as to communicate with the cavity.

However, with the air purging hole communicating with the cavity,foreign matter may enter the cavity from the exterior via an airflowcaused by the expansion/contraction of air. Further, this configurationrequires an operation of closing the hole after a bonding or sealingprocess, and, therefore, foreign matter generated by a material used todose the hole or foreign matter produced in the closing operation mayenter into the inside of the module to cause a flaw in an image.

DISCLOSURE OF INVENTION

In order to solve the above-mentioned conventional problems, it is anobject of the present invention to provide an imaging apparatus thatachieves thickness reduction and an improvement in workability, andallows air circulation between the exterior and a cavity enclosed by asemiconductor imaging device and an optical filter, while suppressingthe entry of foreign matter from the exterior into the cavity via anairflow caused by expansion/contraction of air.

An imaging apparatus according to the present invention includes: athree-dimensional substrate in which a partition wall having an openingat a central portion is formed so as to cross an inner cavity; anoptical filter that is fixed on a first flat surface of both surfaces ofthe partition wall so as to cover the opening; a semiconductor imagingdevice that is face-down mounted on a second flat surface of thepartition wall with an imaging area facing the opening; and an opticalsystem for forming images that is installed on a side of the opticalfilter in the inner cavity of the three-dimensional substrate. Theopening of the partition wall is closed on both sides with the opticalfilter and the semiconductor imaging device so as to form a cavity. Inorder to solve the above-mentioned problems, an air passage for allowingcommunication between the cavity and an exterior of thethree-dimensional substrate is formed on the first flat surface, and hasa labyrinth structure that causes a flow rate of air passing through theair passage to vary depending on a location in the air passage.

According to this configuration, for example, in a heating process forfabricating an imaging apparatus, when gas (air) existing in a cavityexpands/contracts, air circulation is performed only through a passagehaving a non-linear structure, and thus the entry of foreign matter fromthe exterior can be prevented reliably. This can prevent a phenomenon inwhich foreign matter entering from the exterior causes a so-called flawin an image that deteriorates the image, and thus can reduce theoccurrence of a failure in a process resulting from thickness reduction.

The labyrinth structure of the air passage can be defined by a zigzagshape, a shape inclined as a whole or a circular-arc shape.

Furthermore, the labyrinth structure of the air passage may be formed byproviding a rib crossing the air passage so that a height of the airpassage in a thickness direction of the optical filter varies along aflow direction of the air passage. According to this configuration, agap formed between an optical filter and a labyrinth structure varies incross-sectional area along an air passage. Thus, it is possible to causea flow rate of air passing through the air passage to vary with theheight of the gap.

Furthermore, the labyrinth structure of the air passage may be formed byproviding a concave part on a side edge of the air passage so that awidth of the air passage within the first flat surface varies along theflow direction of the air passage. According to this configuration, agap formed between an optical filter and a labyrinth structure varies incross-sectional area along an air passage. Thus, it is possible to causea flow rate of air passing through the air passage to vary with thewidth of the gap.

Preferably, the three-dimensional substrate has such a low lighttransmittance with respect to a region sensitive to light reception bythe semiconductor imaging device that substantially no unwanted signalis generated. According to this configuration, with regard to theachievement of higher sensitivity of semiconductor imaging devices thatis pursued along with the size reduction of imaging apparatuses, aninfluence of disturbance light can be reduced in an imaging apparatus,thus suppressing a functional deterioration of the imaging apparatuswhen used in portable equipment that is used outdoors frequently.Moreover, even when the imaging apparatus is used in so-called skeletontype portable equipment, which is future portable equipment that itselfhas a translucent housing, the entry of light entering from theperiphery can be prevented reliably, making it possible to prevent adeterioration of an image with reliability.

Furthermore, preferably, the air passages are located at a positionaxisymmetric with respect to the opening in the three-dimensionalsubstrate. According to this configuration, anisotropy caused at thetime of heating after a transparent plate is bonded to athree-dimensional substrate can be reduced, and thus it is possible toprevent a decrease in the flatness of a flat surface on which asemiconductor imaging device is mounted. This facilitates the thicknessreduction of imaging apparatuses.

A method for manufacturing an imaging apparatus according to the presentinvention uses a three-dimensional substrate in which a partition wallhaving an opening at a central portion is formed so as to cross an innercavity, an air passage with a non-linear structure for allowingcommunication between the opening and an exterior of thethree-dimensional substrate is formed on a first flat surface of bothsurfaces of the partition wall, and a conductor land for connection isprovided on a second flat surface of the partition wall. The methodincludes process steps of fixing an optical filter on the first flatsurface by bonding; installing a semiconductor imaging device withrespect to the conductor land for connection provided on the second flatsurface; sealing the semiconductor imaging device; and subsequentlyinstalling an optical system for forming images in the inner cavity ofthe three-dimensional substrate.

According to this manufacturing method, since an optical filter is fixedby bonding with respect to a three-dimensional substrate, the mechanicalstrength of the three-dimensional substrate is increased, and thus, in alater process, it becomes easier to secure the accuracy of, for example,a required flatness at the time of mounting a semiconductor imagingdevice. Moreover, by subsequently sealing the semiconductor imagingdevice, the entry of foreign matter into a cavity between thesemiconductor imaging device and the optical filter can be preventedreliably. This prevents a phenomenon in which foreign matter in animaging apparatus causes a flaw, thereby facilitating the size andthickness reduction of imaging apparatuses.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an imaging apparatus according to anembodiment of the present invention.

FIG. 2 is a cross-sectional view of the imaging apparatus along a lineX-X of FIG. 1.

FIG. 3 is an enlarged view of a portion denoted A in FIG. 2.

FIG. 4A is a diagram showing characteristics of the imaging apparatusaccording to the embodiment of the present invention with respect tolight wavelengths, specifically, the sensitivity of a semiconductorimaging device with respect to light wavelengths; FIG. 4B is a diagramshowing the transmittance of an optical filter with respect to lightwavelengths; and FIG. 4C is a diagram showing the transmittance of athree-dimensional substrate with respect to light wavelengths.

FIG. 5 is an exploded perspective view of an important portion showingthe relationships among the optical filter, the three-dimensionalsubstrate and the semiconductor imaging device in the embodiment of thepresent invention.

FIGS. 6A to 6F are perspective views respectively showing other examplesof the shape of an air passage provided on a partition wall according tothe embodiment of the present invention.

FIG. 7 is a diagram showing a flow of fabricating the imaging apparatusaccording to the embodiment of the present invention.

DESCRIPTION OF THE INVENTION

In the imaging apparatus according to the present invention, the openingof the three-dimensional substrate is enclosed with the optical filterand the semiconductor imaging device so as to form a cavity, and the airpassage for allowing the cavity to communicate with the exterior has thelabyrinth structure that causes a flow rate of air passing through theair passage to vary depending on a location in the air passage. Thus,for example, in a process of fabricating an imaging apparatus, the entryof foreign matter into a module can be prevented, thereby facilitatingthickness reduction and improving workability in fabrication.

Hereinafter, the present invention will be described by way of anembodiment with reference to the appended drawings. Referring first toFIGS. 1 to 3, the description is directed to the configuration of animaging apparatus according to this embodiment.

FIG. 1 is a perspective view of the imaging apparatus. Athree-dimensional substrate 1 is composed of a base part 7 having arectangular planar shape and a cylindrical barrel part 17 provided onthe base part 7. The three-dimensional substrate 1 is formed from aglass reinforced PPA (polyphthalamide resin) or the like and is tintedblack so as to prevent the transmission of external light therethrough.For the connection to the exterior, a terminal part 7 a is provided onan outer side of the base part 7 of the three-dimensional substrate 1.AFPC (flexible printed circuit board) 15 for transmitting signals to andreceiving signals from external equipment is disposed on a lower side ofthe base part 7, and a connection land 15 a formed on the FPC 15 isconnected to the terminal part 7 a using solder 16. A lens 2 that ismade of resin and fitted into a lens holder 20 is disposed in an innercavity of the barrel part 17 of the three-dimensional substrate 1. Thelens holder 20 is fixed on an outer side of the barrel part 17 by meansof an adjusting ring 21 disposed on an outer side of the lens holder 20.The lens holder 20 is provided with a diaphragm 3. A semiconductorimaging device 4 and an optical filter 5 that suppresses the sensitivityto light in the infrared region are disposed on a boundary between thebase part 7 and the barrel part 17.

The following describes the structure of the imaging apparatus infurther detail with reference to FIGS. 2 and 3. FIG. 2 is across-sectional view of the imaging apparatus shown in FIG. 1 taken online X-X FIG. 3 is an enlarged view of a portion denoted A in FIG. 2. Apartition wall 11 is formed on a boundary between the base part 7 andthe barrel part 17. An opening 10 a is formed at a central portion ofthe partition wall 11, and upper and lower surfaces of the partitionwall 11 that enclose the opening 10 a respectively form a first flatsurface 12 and a second flat surface 13 that are parallel to each other.The optical filter 5 is disposed on the first flat surface 12 on anupper side, and the semiconductor imaging device 4 as well as a chipcomponent and the like that are not shown is disposed on the second flatsurface 13 on a lower side. The optical filter 5 is fixed in apredetermined position on the first flat surface 12 using an adhesive 6.The opening 10 a is formed in a rectangular shape so as to correspond toan imaging area of the semiconductor imaging device 4 that will bedescribed later. All of these constituent components are assembled onthe three-dimensional substrate 1.

As shown in FIG. 3, a wiring pattern 7 b is formed on a back side of thebase part 7 by electroless plating or the like. On an inner side of thesecond flat surface 13 in the three-dimensional substrate 1, aconnection land 7 c for bare-chip mounting the semiconductor imagingdevice 4 is provided. The connection land 7 c is connected to theterminal part 7 a by means of the wiring pattern 7 b.

The semiconductor imaging device 4 is formed of, for example, aso-called ⅙-inch VGA CCD with about 320,000 pixels and face-down mountedwith respect to the connection land 7 c so as to be connectedelectrically to the connection land 7 c. This is intended to performbare-chip mounting using no package, thereby realizing the thicknessreduction of the imaging apparatus. Face-down mounting is performed by,for example, so-called SBB Stud Bump Bond) that is a c connection methodusing a bump 8 formed from gold and an Ag paste 8 a that is a conductiveadhesive containing silver as a conductive material and applied on thetip of the bump 8. The semiconductor imaging device 4, after beingface-down mounted, is sealed with a sealant 9. An electric wiring isformed via the wiring pattern 7 b and the connection land 15 a of theFPC 15 (see FIG. 1), and used for the output of image signals to theexterior, which are obtained by the semiconductor imaging device 4 andthe chip component and the like that are not shown, a control signalfrom the exterior, and power supply. Metal foil 14 (see FIG. 2) isattached on a back surface of the FPC 15 so as to prevent the entry ofvisible light and infrared light from the back surface into thesemiconductor imaging device 4.

On the first flat surface 12 of the opening 10 a provided in thethree-dimensional substrate 1, on which the optical filter 5 isinstalled, an air passage 12 a having a labyrinth structure is formed ata position axisymmetric with respect to the opening 10 a. After theoptical filter 5 and the semiconductor imaging device 4 are installed,the opening 10 a constitutes a cavity 10, and air travels between thecavity 10 and the exterior only through the air passage 12 a.

The lens 2 housed in the barrel part 17 is composed of two asphericallenses (hereinafter, abbreviated as lenses) 2 a and 2 b that havedifferent optical characteristics from each other and are fitted intothe lens holder 20 in such a manner that constant positionalrelationship between them can be maintained. On an outer periphery ofthe lens holder 20 and on an inner periphery of the adjusting ring 21disposed on the outer side of the lens holder 20, screws 20 a and 21 athat engage with each other are formed, respectively, so that theposition of the lens holder 20 in an axial direction can be adjusted.

The description is directed next to an optical system of the imagingapparatus according to this embodiment with the above-describedconfiguration. Light from a subject passes through the diaphragm 3provided at a center of the lens holder 20 to be focused by the lens 2,passes through the optical filter 5, and enters the semiconductorimaging element 4 to form an image. The diaphragm 3 is designed to havean aperture increasing in a direction toward the side of the subject.This is intended to prevent a phenomenon in which light entering towardthe lens impinges on a wall surface in an optical axis direction of thediaphragm 3 to be diffused and enters the lens as unwanted light.

The lens 2 is formed from a resin that can satisfy required opticalcharacteristics such as a transmittance, a refractive index and thelike. This embodiment uses a lens as an example that is formed byinjection molding using “ZEONEX” (trade name) manufactured by ZEONCorporation. For example, the lens 2 is composed of two lenses andachieves a so-called pan-focus that allows an image to be formed at adistance farther than a given distance. In this embodiment, for example,the lens 2 is set so that focus is achieved with respect to a subject ata distance farther than a distance of about 30 cm. These configurationsand characteristics can be selected suitably.

The optical filter 5 suppresses the transmission of light in a regionother than the visible light region. In this embodiment, for example,borosilicate glass is used as a base material so that ultraviolet lightis cut off. A filter that has one surface coated with an IR (Infra Red)cut-off coat and the other surface coated with an AR (Anti Reflection)coat for preventing reflection can be used. The optical filter 5according to this embodiment has spectral characteristics shown in FIG.4B, for example. The optical filter 5 is set to have a transmittance ofapproximately 93% or higher with respect to light with a wavelength in avisible light region of about 400 nm to 600 nm and a sufficiently lowtransmittance with respect to light with a wavelength in a region otherthan the visible light region. The spectral characteristics also can bechanged suitably. As the IR cut-off coat, for example, a film of silicondioxide (SiO₂), titanium oxide (TiO₂) or the like is formed on glass byvapor deposition. As the AR coat for preventing reflection, for example,a film of magnesium fluoride (MgF₂), titanium oxide (TiO₂), zirconiumoxide (ZrO₂) or the like is formed by vapor deposition. With respect toeach of the IR cut-off coat and the AR coat, a film configuration andthe number of layers to be laminated can be selected suitably dependingon characteristics of suppressing transmission/reflection of light inthe visible light region and light in a region other than the visiblelight region.

The adhesive 6 for bonding the optical filter 5 is formed from, forexample, a UV thermosetting adhesive that uses an epoxy resin as a basematerial. It is desirable to select a material for the adhesive 6 thathas a coefficient of linear expansion in a range between the coefficientof linear expansion of the three-dimensional substrate 1 and thecoefficient of linear expansion of the optical filter 5. This isintended to reduce stress to be exerted on the three-dimensionalsubstrate 1 and the optical filter 5 at the time of heating, which isperformed generally in a bonding/curing process, thereby preventing adeterioration of, for example, the flatness with respect to a mountingsurface due to warping or the like. In this embodiment, for example, thethree-dimensional substrate 1 has a coefficient of linear expansion ofapproximately 40×10⁻⁶mm/mm° C., and the optical filter 5 has acoefficient of linear expansion of about 10×10⁻⁶mm/mm° C. The adhesive 6of an epoxy resin for fixing these components is adjusted to have acoefficient of linear expansion in the range between these coefficientvalues through adjustment of the content of a filler (not shown).

An infrared light component and an ultraviolet light component of lightfrom a subject are cut off/absorbed by the optical filter 5, and thusonly a visible light component of the light enters the semiconductorimagining device 4. The incident light component passes through knownso-called micro lenses or on-chip lenses provided on a surface of alight-receiving surface of the semiconductor imaging device 4, which arenot shown, passes through a color filter that is a color system providedbelow the lenses, and is converted into the required electric signal bya photodiode. As a result, for example, an image signal in a frame rateof 30 frames per second with an aspect ratio of a screen of 4:3 isoutput.

As described above, the semiconductor imaging device 4 is face-downmounted in the form of a bare chip using no package so that the imagingapparatus has a reduced thickness. Moreover, the semiconductor imagingdevice 4 itself further is ground from a back surface side so as to havea thickness reduced to about 0.7 mm. As is apparent also from FIG. 2,the thickness of the imaging apparatus can be reduced as much as thethickness of the semiconductor imaging device 4 is reduced. Therefore,it is highly effective in reducing the thickness of an imaging apparatusto use a wafer having a reduced thickness. In view of the fact that acolor filter, an aluminum wiring, a photodiode and the like that areprovided on a lower side of micro lenses have a thickness of at mostabout several tens of microns, a wafer having a further reducedthickness can be used. However, it is desirable that the thickness of awafer be determined suitably taking into consideration the magnitude ofan external force exerted due to, for example, mounting equipment or thelike being handled and the respective parameters of the flatness,mechanical strength and the like of the wafer itself. In addition, inthe case where the semiconductor imaging device 4 is reduced inthickness, deterioration of an image may be caused particularly by lightwith a long wavelength that enters from a back surface, and thus it isdesirable that, as in this embodiment, measures should be taken toprevent such a deterioration by, for example, shielding the back surfacefrom light with the metal foil 14 or the like.

An end surface 10 b facing the opening 10 a is configured so that anarea of the opening is increased toward the side of the semiconductorimaging device 4. Similarly to the above-described diaphragm 3, this isintended to prevent a phenomenon in which light that has impinged on theend surface 10 b of the opening is diffused and enters the lens again asunwanted light. Although it also is possible to prevent this phenomenonby roughening the end surface or applying a matte coating for preventingreflection on the end surface, with the configuration according to thisembodiment, it is only required to provide a needed taper on a mold forforming the three-dimensional substrate 1 made of resin by injectionmolding, thus eliminating the need to roughen the end surface or applythe matte coating. In the injection molding, this tapered portion can beutilized as a releasing taper, and thus the above-describedconfiguration further is effective in obtaining excellent moldabilityand mold releasability at the time of molding. The imaging apparatusaccording to this embodiment is manufactured by processes in which theoptical filter 5 and the semiconductor imaging device 4 are mounted onthe three-dimensional substrate 1 so as to be formed into a module, andthen the optical system is fabricated. It is desirable that theabove-described fabrication be performed in an environment with highcleanliness.

The description is directed next to the light transmittance in thethree-dimensional substrate 1 with reference to FIG. 4. FIG. 4A showsthe sensitivity of the semiconductor imaging device 4 with respect towavelengths in this embodiment. The semiconductor imaging device 4according to this embodiment is formed from silicon, and an upper limitvalue on a long wavelength side in a sensitivity region of thesemiconductor imaging device 4 is determined by a wavelength defined bythe band gap energy (Eg) of silicon. Silicon generally has a band gapenergy of about 1.12 eV at room temperature. Further, it is known that alimit value of a wavelength can be determined by λ≈1,240/Eg, and thus alimit value on a long wavelength side of about 1,100 nm is obtained. Onthe other hand, the sensitivity on a short wavelength side extends to avalue as short as about 200 nm in the ultraviolet region.

FIG. 4B shows the transmittance of the optical filter 5 with respect towavelengths. The optical filter 5 is formed from borosilicate lead glassas a base material and thus is provided with a characteristic ofabsorbing light in the ultraviolet region. With respect to a longwavelength side, the transmission of light in the infrared region issuppressed by the above-described IR cut-off coat. These twocharacteristics allow only the transmittance of light in the visibleregion to be increased.

FIG. 4C shows the transmittance of the three-dimensional substrate 1with respect to wavelengths. The three-dimensional substrate 1 is set tohave a light transmittance that is sufficiently low with respect to asensitivity region of the semiconductor imaging device 4. Specifically,carbon black and glass fiber are added to the resin material (PPA) ofthe three-dimensional substrate 1. Carbon black is effective withrespect to visible light and light on a short wavelength side and hasexcellent dispersibility. Further, with respect to light on a wavelengthside longer than a wavelength of visible light, in order to control thelight transmittance, a slight amount of a metal filler that has a highthermal conductivity is used or a resin material of an increasedthickness is used for the three-dimensional substrate 1. These methodsof controlling the transmittance can be selected suitably depending onthe degree of an influence on an image.

In the above-described manner, the light transmittance of thethree-dimensional substrate 1 is adjusted so as to be low with respectto a region sensitive to light reception by the semiconductor imagingdevice 4. Thus, even in the case where the imaging apparatus is mountedin portable equipment or the like and thus possibly is used outdoorsfrequently, deterioration of an image caused by light entering from theperiphery can be prevented reliably. Moreover, even in the case wherethe imaging apparatus is used in so-called skeleton type portableequipment, which is future portable equipment that itself has atranslucent housing, the entry of light entering from the periphery canbe prevented reliably, making it possible to prevent a deterioration ofan image with reliability.

Next, the air passage having the labyrinth structure will be describedin detail with reference to FIG. 5. FIG. 5 is an exploded perspectiveview of an important portion showing the relationships among the opticalfilter 5, the three-dimensional substrate 1 and the semiconductorimaging device 4. Although the partition wall 11 is shown to have arectangular shape for the sake of convenience, a peripheral portion ofthe partition wall 11 actually is continuous to the other portion of thethree-dimensional substrate 1. On the first flat surface 12 of thepartition wall 11 that is positioned on a boundary between the base part7 and the barrel part 17 of the three-dimensional substrate 1 and formsthe opening 10 a, the air passages 12 a having the labyrinth structureare provided at a position axisymmetric with respect to the opening 10a. An amount of an airflow that passes through the labyrinth structurevaries depending on a location in the labyrinth structure. Based onBernoulli's theorem, a variation in the amount of airflow causes avariation in pressure, so that foreign matter is trapped whiletraveling. This embodiment makes positive use of this phenomenon. Thelabyrinth structure according to this embodiment has a zigzag shape. Agroove of the labyrinth structure has a width of 0.13 mm and a depth of0.04 mm. One end of the groove reaches the opening 10 a and the otherend extends beyond an outer periphery of the optical filter 5 installedon the first flat surface 12. It is desirable that the other end of thegroove be positioned in such a manner as to allow an enough margin withrespect to a deviation of a position of the installed optical filter 5.

In the semiconductor imaging device 4, an electric signal of an imageobtained from an imaging area 4 a in which effective pixels are arrangedis led out to a Pad part 4 b disposed on a periphery by means of aninternal wiring formed from aluminum or the like, which is not shown. Onthe Pad part 4 b, a gold wire formed into a required shape is providedas the bump 8 by a bump bonder. The bump 8 is used to establish anelectrical connection between the three-dimensional substrate 1 and theconnection land 7 c. Although it also should be noted that the bump havean optimum shape according to the flatness of the second flat surface 13and a joining method, detailed description thereof is omitted.

The air passage 12 a has a zigzag shape and thus is set so that a flowrate of air passing therethrough varies depending on a location in theair passage 12 a. Based on Bernoulli's principle, a variation in theflow rate causes a variation in pressure. Due to this variation inpressure, foreign matter being entrained in air flowing in/out iscaptured in the air passage 12 a. As described above, in a modulefabricated in an environment with high cleanliness, the cavity 10 formedas a result of enclosing the opening 10 a is assumed to be free fromforeign matter. Air in the opening 10 may flow in/out depending ontemperature and pressure differences from those of ambient air. However,since foreign matter contained in the air flowing in is captured by theair passage 12 a, the cavity 10 always is kept in a state of being freefrom foreign matter.

As described above, in fabricating an imaging apparatus, beforefabricating an optical system, the optical filter 5 and thesemiconductor imaging device 4 are installed on the three-dimensionalsubstrate 1. A bonding or sealing process in this fabrication includesheating/cooling an entire module, which causes expansion/contraction ofair in the cavity 10. If the air in the cavity 10 does not flow in fromand out to the exterior, an internal pressure increases to cause asealant to be pushed away, so that sealing at a predetermined positionmay be hindered in the fabrication of the module, and moreover, anincrease in the internal pressure also may cause the optical filter 5 tobe broken, which have been disadvantageous. In order to avoid this, in aknown conventional method, an air purging hole is provided However, thismethod requires an operation of dosing the hole at a later stage, andforeign matter generated by a material used to dose the hole or foreignmatter produced in the dosing operation may enter the cavity 10, whichhas been disadvantageous. Further, in curing equipment used for curing asealant or an adhesive, although full attention is paid to keeping thecleanliness of the environment, due to dust generated when the sealantor the adhesive is cured, foreign matter is likely to be presentcompared with other dean environments, and thus cleanliness tends belowered. Under this environment, when air in the cavity 10 expands andthen contracts, surrounding air is taken into the cavity. Against suchair movement, the provision of an air passage can prevent the entry offoreign matter reliably. This can prevent reliably the adherence offoreign matter to the surface of the semiconductor imaging device 4,which is most likely to have an influence on image quality, therebyallowing a more reliable imaging apparatus to be obtained.

It is known that an image is influenced most by foreign matter thatadheres to the above-described micro lenses provided on the surface ofthe semiconductor imaging device 4. This is because such foreign matterblocks light from being incident on the photodiode of the semiconductorimaging device 4, and thus directly causing an output decrease. Further,foreign matter of a size equivalent to a pixel size surely affects animage as a flaw, and thus exerting a particularly large influence.

An examination of the influence of foreign matter on an image in thisembodiment was performed and found that, with respect to foreign matterof almost the same size, an influence exerted by foreign matter that waspresent on the surface of the semiconductor imaging device 4 was aslarge as about 40 times an influence exerted by foreign matter on anupper surface of the optical filter 5 (surface on a lens side). Althoughthe degree of an influence may vary depending on conditions of theoptical system, this explains how largely an image could be influencedby foreign matter that adheres to the surface of the semiconductorimaging device 4. Since there is a possibility that foreign matter thatis present in the cavity 10 adheres to the surface of the semiconductorimaging device 4, it is extremely important that the entry of foreignmatter into the cavity 10 is prevented.

With an increasing demand for smaller imaging apparatuses with higherquality, it also has become necessary that the semiconductor imagingdevice 4 is bare-chip mounted. Therefore, in order to achieve thicknessreduction without deteriorating reliability, it is effective thatforeign matter entrained in air flowing in/out of the cavity 10 iscaptured by the air passage 12 a having the labyrinth structure.

The labyrinth structure of the air passage 12 a according to thisembodiment has a zigzag shape extending linearly from a center of theopening 10 to an outer side. However, the labyrinth structure may have ashape inclined as a whole such as of an air passage 12 b shown in FIG.6A or a circular-arc shape such as of an air passage 12 c shown in FIG.6B. Further, the groove of the labyrinth structure may have a width anda depth that vary depending on a location in the labyrinth structure.Also in these cases, in order not to incur a cost increase, it ispreferable that the air passage 12 a is shaped using a mold for formingthe three-dimensional substrate 1 by resin molding. As described above,the labyrinth structure according to this embodiment can be defined as astructure in which the air passage 12 a has a planar shape such that aflow rate of air passing through the air passage 12 a varies dependingon a location in the air passage 12 a.

With the air passages 12 a provided at a position axisymmetric withrespect to the opening 10 a, stress generated due to, for example,thermal stress exerted when the optical filter 5 is fixed on the firstflat surface 12 by bonding can be adjusted so as to be balanced withrespect to the opening 10 a. Thus, a deterioration of the flatness ofthe second flat surface 13 for mounting the semiconductor imaging device4 can be prevented reliably. Generally, in the case where thesemiconductor imaging device 4 is face-down mounted on the second flatsurface 13 by a connection method such as BGA (Ball Grid array) or SBB,the flatness of a portion used for connection should be suppressed toabout half the height of the bump 8, and it is desirable that theflatness be not more than about 30 μm. Therefore, it is necessary tominimize factors that deteriorate the flatness of the second flatsurface 13.

The description is directed next to a labyrinth structure of an airpassage according to another embodiment with reference to FIGS. 6C to6F. An air passage 12 d shown in FIG. 6C is provided with ribs 18. Sincethe ribs 18 are present, the height of the air passage 12 d with respectto a thickness direction of the optical filter 5 varies along a flowpath. FIG. 6D shows an enlarged view of the ribs 18. According to thisstructure, a gap formed between the optical filter 5 and the labyrinthstructure varies in cross-sectional area along the air passage 12 d.This can cause a flow rate of air passing through the air passage 12 dto vary with the height of the gap.

The gap formed between an upper surface of the ribs 18 and the opticalfilter 5 has, for example, a minimum size of 30 μm and a width of 0.4mm. These dimensions can be selected suitably according tocharacteristics of a semiconductor imaging device, a pixel size,manufacturing conditions used in processes and the like. Moreover, theribs 18 have a shape tapered toward a tip portion. This shape isemployed in consideration of the following. That is, when forming thethree-dimensional substrate 1 by injection molding, this shape can beobtained using a so-called impression formed in a mold. Further, thisshape provides the effect of allowing a releasing taper to be formed soas to improve mold releasability.

FIG. 6E shows an embodiment in which the ribs 18 shown in FIG. 6D ismodified. A labyrinth structure in this case has ribs 18 a to 18 c. Theribs 18 a to 18 c have a height decreased in this order. According tothis structure, the ribs 18 a to 18 c have a height varying depending ona position in a flow direction of an air passage. This can cause a flowrate to vary in a larger degree, and thus foreign matter is capturedmore effectively. The order of arrangement of the respective heights ofthe ribs 18 a to 18 c can be changed suitably. Further, it is preferablethat, similarly to the ribs 18 shown in FIG. 6D, the ribs 18 a to 18chave a shape that can be obtained using a so-called impression formed ina mold and provides the effect of allowing a releasing taper to beformed so as to improve mold releasability.

In a labyrinth structure of an air passage 12 e shown in FIG. 6F, aconcave part 19 a is formed on a side edge of the air passage 12 e inthe first flat surface 12. With the concave part 19 a, while the heightof the air passage 12 e does not vary with respect to the thicknessdirection of the optical filter 5, the width of the air passage 12 evaries along a flow direction. This allows a gap formed between theoptical filter 5 and the labyrinth structure to vary in the area of across section orthogonal to a direction of an airflow. According to thisconfiguration, a flow rate of air passing through the air passage 12 evaries with a cross-sectional area, and thus foreign matter is captured.In a position of the concave part 19 a, a deeper concave part 19 b maybe provided so that foreign matter that has been captured is capturedsecurely by the deep concave part 19 b.

The concave part 19 a has a depth of, for example, 50 μm, and the widthof the air passage 12 e is, for example, 0.4 mm at the widest point anda 0.15 mm at the narrowest point. Moreover, the deep concave 19 b has acylinder shape that is, for example, 0.15 mm in depth and 0.15 mm indiameter. These dimensions can be selected suitably according tocharacteristics of a semiconductor imaging device, a pixel size,manufacturing conditions used in processes and the like.

It also is possible to use the labyrinth structures according to theabove-described embodiments in combination so as to allow greater designfreedom. For example, the ribs 18 shown in FIG. 6D may be arranged in aportion of the concave part 19 a in the labyrinth structure shown inFIG. 6F so that a variation in height is obtained

The description is directed next to a method for manufacturing theimaging apparatus according to this embodiment with reference to FIG. 7and FIGS. 1 to 3. FIG. 7 is a diagram showing a flow of fabricating animportant portion of the module prior to the installation of the opticalsystem, in which the semiconductor imaging device 4 is mounted on thethree-dimensional substrate 1 as described above. In the figure, processsteps that are not related directly to this embodiment are omitted. StepS30 to S35 are process steps up to the fabrication of the optical filter5 on the three-dimensional substrate 1. Steps S36 to S38 are processsteps in which the semiconductor imaging device 4 is prepared to bemounted on the three-dimensional substrate 1. Steps S40 to S43 areprocess steps from a step of finishing mounting with respect to thethree-dimensional substrate 1 to a step of completing the module.

First, in a pretreatment performed in Step S30, the three-dimensionalsubstrate is subjected to baking and cleaning so that moisture containedin a slight amount in the three-dimensional substrate is eliminated. Itis preferable that, particularly, conditions for eliminating moistureare determined based on an evaluation of a final product, though theyalso may depend on heating conditions. Next, in Step S31, the opticalfilter 5 that has been cleaned is placed in a desired position on thefirst flat surface 12 of the three-dimensional substrate 1. At thistime, as well as positioning of the optical filter 5, a front or back ofthe optical filter 5 is checked as necessary. Next, in Step 32, a fixedamount of the adhesive 6 made of a UV thermosetting epoxy resin forfixing the optical filter 5 to the three-dimensional substrate 1 isapplied using a dispenser. Next, in Step 33, the adhesive 6 isirradiated with UV light. This allows a cure initiator contained in theadhesive to be activated to start curing. Next, in Step S34, heating isperformed at 150° C. so that the curing of the adhesive 6 that has beeninitiated using the UV light is performed completely. Thus, the opticalfilter 5 is fixed at the desired position of the three-dimensionalsubstrate 1. Next, in Step S35, the three-dimensional substrate 1 onwhich the optical filter 5 is fixed is turned upside down and set inequipment for mounting the semiconductor imaging device 4.

The following describes the process steps in which the semiconductorimaging device 4 is prepared for mounting. In Step S36, the bump 8 forconnection is bonded to the Pad part 4 b of a bare chip that is formedby dicing of a wafer and constitutes the semiconductor imaging device 4.To this end, a gold wire is heated and discharged from a nozzle referredto as a capillary so as to form the bump 8. Next, in Step S37, a tipportion of the bump 8 is deformed plastically so that the bump 8 isadjusted to have a predetermined height. Next, in Step 38, as aconductive adhesive for electrically connecting the bump 8 and theconnection land 7 c of the three-dimensional substrate 1, an Ag paste istransferred onto the tip portion of the bump 8. Since connectionreliability may be affected by the shape of the tip portion of the bump8, the viscosity and conductivity the Ag paste, and the like, it isdesirable that full consideration be given in setting conditions.

The following describes the process steps from a step of mounting thesemiconductor imaging element 4 to the step of completing the module. InStep S40, using a pattern recognizer or the like, positioning isperformed so that the semiconductor imaging device 4 and the connectionland 7 c of the three-dimensional substrate 1 are aligned with respectto each other, and the semiconductor imaging device 4 is placed on thesecond flat surface 13 of the three-dimensional substrate 1. Next, inStep 41, the Ag paste on the tip portion of the bump 8 provided on thesemiconductor imaging device 4 is cured by heating at 80° C. Next, inStep S42, a sealant for shielding the semiconductor imaging device 4from ambient air is applied. Next, in Step 43, the sealant is cured byheating at 125° C. Temperature conditions for these process steps can beselected suitably depending on an adhesive, equipment and the like thatare used.

According to the above-described process steps, the optical filter 5 isfixed with respect to the three-dimensional substrate 1, and thus themechanical strength of the three-dimensional substrate 1 can beincreased. With an increase in the mechanical strength, high accuracy ofthe flatness of the second flat surface 13 for mounting thesemiconductor imaging device 4 can be maintained. In other words, with aconfiguration in which the optical filter 5 is fixed so that thethree-dimensional substrate 1 has a mechanical strength equal to that inthe conventional case, the three-dimensional substrate 1 further can bereduced in thickness, thereby enhancing the thickness reduction of theimaging apparatus.

Furthermore, in heating processes performed in Steps S41 to 43, air inthe cavity 10 expands/contracts. According to this embodiment, the airin the cavity 10 can flow in and out by means of the air passage 12 a.Therefore, an internal pressure of the cavity 10 does not increase, andthus a phenomenon is avoided in which a sealant is pushed away, so thatsealing at a predetermined position is hindered in the fabrication ofthe module and moreover, the optical filter 5 breaks. In addition, theair passage 12 having the labyrinth structure, while allowing air toflow in and out, prevents the entry of foreign matter reliably, and thusthe adherence of the foreign matter to the surface of the semiconductorimaging device 4 can be prevented reliably. This facilitates thethickness reduction of imaging apparatuses.

INDUSTRIAL APPLICABILITY

The imaging apparatus according to the present invention can prevent theentry of foreign matter into a module in, for example, a process offabricating the apparatus, facilitates the thickness reduction of theapparatus, and has a structure that improves workability in fabrication.Thus, the imaging apparatus can be used favorably in a camera mounted inportable equipment or the like.

1. An imaging apparatus, comprising: a three-dimensional substrate inwhich a partition wall having an opening at a central portion is formedso as to cross an inner cavity; an optical filter that is fixed on afirst flat surface of both surfaces of the partition wall so as to coverthe opening; a semiconductor imaging device that is face-down mounted ona second flat surface of the partition wall with an imaging area facingthe opening; and an optical system for forming images that is installedon a side of the optical filter in the inner cavity of thethree-dimensional substrate, the opening of the partition wall beingclosed on both sides with the optical filter and the semiconductorimaging device so as to form a cavity, wherein an air passage forallowing communication between the cavity and an exterior of thethree-dimensional substrate is formed on the first flat surface, and hasa labyrinth structure that causes a flow rate of air passing through theair passage to vary depending on a location in the air passage.
 2. Theimaging apparatus according to claim 1, wherein the labyrinth structureof the air passage is defined by a zigzag shape, a shape inclined as awhole or a circular-arc shape.
 3. The imaging apparatus according toclaim 1, wherein the labyrinth structure of the air passage is formed byproviding a rib crossing the air passage so that a height of the airpassage in a thickness direction of the optical filter varies along aflow direction of the air passage.
 4. The imaging apparatus according toclaim 1, wherein the labyrinth structure of the air passage is formed byproviding a concave part on a side edge of the air passage so that awidth of the air passage within the first flat surface varies along theflow direction of the air passage.
 5. The imaging apparatus according toclaim 1, wherein the three-dimensional substrate has such a low lighttransmittance with respect to a region sensitive to light reception bythe semiconductor imaging device that substantially no unwanted signalis generated.
 6. The imaging apparatus according to claim 1, wherein theair passages are located at a position axisymmetric with respect to theopening in the three-dimensional substrate.
 7. A method formanufacturing an imaging apparatus that uses a three-dimensionalsubstrate in which a partition wall having an opening at a centralportion is formed so as to cross an inner cavity, an air passage with anon-linear structure for allowing communication between the opening andan exterior of the three-dimensional substrate is formed on a first flatsurface of both surfaces of the partition wall, and a conductor land forconnection is provided on a second flat surface of the partition wall,comprising process steps of: fixing an optical filter on the first flatsurface by bonding; installing a semiconductor imaging device withrespect to the conductor land for connection provided on the second flatsurface; sealing the semiconductor imaging device; and subsequentlyinstalling an optical system for forming images in the inner cavity ofthe three-dimensional substrate.